I have a very weak machine (i486 with 512 MB of RAM) and want to install last Ubuntu server release on it. When I try to install ubuntu server 11.10 (32 bit) , installer says the architecture needed is i586 but only found CPU is an i486.
If there is no i486 ubuntu available, how can I recompile kernel with i486 optimization and replace it with default kernel of installer?
If you want Ubuntu you need a server version from before Ubuntu Maverick Meerkat 10.10. Meerkat dropped i486 support. 10.04 is an LTS and has support up to 2015 so you are still safe for a few years!
Besides older Ubuntu versions there are other options ... Distrowatch can help you with what you are searching for. The link shows Server versions with i486 architecture for Linux. You do need to check the minimum specifications for each Distro though!
Result from the link that should be promising:
Gentoo Linux
Gentoo Linux is a versatile and fast, completely free Linux distribution geared towards developers and network professionals. Unlike other distros, Gentoo Linux has an advanced package management system called Portage. Portage is a true ports system in the tradition of BSD ports, but is Python-based and sports a number of advanced features including dependencies, fine-grained package management, "fake" (OpenBSD-style) installs, safe unmerging, system profiles, virtual packages, config file management, and more.
Slackware Linux
The Official Release of Slackware Linux by Patrick Volkerding is an advanced Linux operating system, designed with the twin goals of ease of use and stability as top priorities. Including the latest popular software while retaining a sense of tradition, providing simplicity and ease of use alongside flexibility and power, Slackware brings the best of all worlds to the table. Originally developed by Linus Torvalds in 1991, the UNIX-like Linux operating system now benefits from the contributions of millions of users and developers around the world. Slackware Linux provides new and experienced users alike with a fully-featured system, equipped to serve in any capacity from desktop workstation to machine-room server. Web, ftp, and email servers are ready to go out of the box, as are a wide selection of popular desktop environments. A full range of development tools, editors, and current libraries is included for users who wish to develop or compile additional software.
Superb Mini Server
Superb Mini Server (SMS) is a Slackware-based server distribution with web, DNS, DHCP, file, print and fax servers, iptables firewall, mail server with spam filter and anti-virus scanner, and BitTorrent station. It also includes Webmin, a web-based administration tool, but no graphical desktop. SMS, which comes with Slackware's text-mode system installer, is built using Linux-Live scripts (from Slax) and can be used as a live CD for testing purposes.
Other good options:
You can try Ubuntu 8.04 http://cdimage.ubuntu.com/releases/8.04/release/ or even more recent http://old-releases.ubuntu.com/releases/karmic/
Wow, even when Pentiums came out, 128 mb was a huge amount of ram. I didn't think there were any 486 motherboards that supported more than 16 or 32 mb.
You will need to compile the kernel yourself on another machine. You can get the source with
apt-get source linux. You will want to change the target processor ( withmake menuconfig). Once the kernel is built and installed, you will need to make a corresponding initramfs (update-initramfs). I would say put the Ubuntu installer, the custom kernel and initramfs on a usb flash drive, but such an old computer probably can't boot from usb.I have a number of i486 machines with RAM configs ranging from 256MB to 512MB. I've used Ubuntu Server up to 10.10, S-M-S, and Debian Lenny without any problems. Since these examples are command line based, it saves on resources versus a GUI. So Rinzwind pointed out in explanation will be just fine. Good luck! ;)